I have a Linux server hosting our bug tracking software (CentOS 5.2 Kernel 2.6.18-128.4.1.el5) that I have having some strange network problems with. The machine is configured with two NICS, one for the public interface and the other for our server back end network.

The problem is that after doing a service network restart I can ping the public interface and it sends anywhere from 200-500 ICMP packets and then all of a sudden I start getting a request timed out error. Strange but as soon as I connect to the private interface the ping starts working again to the public interface. I clearly have a routing issue somewhere.

I have a Juniper Router with the following configuration.

Interface 0/0 -- Connect subnet to the ISP at our co-location
Interface 0/2 -- For our DRAC network
Interface 0/3 -- The Server-backend network (plugs directly into a switch that feeds to all the NICs that are on the 10.3.20.x network.
Interface 0/4 -- Plugs directly into another switch that feeds our public interfaces, that interface as all the gateways from our public ip rangs as secondary IP addresses.

I hope that someone can ask the right questions that can lead me to check things and figure out what is going on. Has anyone had similar problems and what kind of things should I be checking? Routing issue or something even more complicated?

Start tcpdump on your public interface, check if you lose incoming or outgoing. Also start another tcpdump on the private interface to make sure the responses don't try to go out that way.
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Max AlgininNov 9 '09 at 17:10

We have the same issue. Were are on RHEL 5.3, 2.6.18-128.el5
We had an issue with our route to our private network. It kept dropping.
We found a work around. We put this in our crontab and this fixes the issue.
* * * * * /sbin/arp -d IP to storage

Have experienced an issue with the linux kernel with the realtek driver on certain boards where watchdog timeouts would cause network interfaces to stop working. The only way was to reset networking and/or modprobe the ko file for the module.
Check /var/log/messages for any such messages.